The present invention relates to a control device for an engine, particularly to a control device which controls an engine based on an operating state of a vehicle.
Conventionally, devices for controlling, when a behavior of a vehicle becomes unstable due to slippage, etc., the behavior of the vehicle toward a safe direction (e.g., sideslip preventing device), are known. Specifically, devices for detecting a behavior, such as understeering or oversteering, in the vehicle when, for example, the vehicle corners, and applying a suitable deceleration to wheels so as to suppress the detected behavior, are known.
On the other hand, as opposed to such a control for improving safety under a traveling state where the vehicle behavior becomes unstable, vehicle operation control devices are known which control a load on front wheels (drive wheels) by adjusting a deceleration when the vehicle corners, so that a series of operations performed by a driver (braking, turning of steering, accelerating, and turning back the steering, etc.) in a normal traveling state of the vehicle becomes natural and stable. For example, JP2011-088576A discloses such a device.
Further, vehicle behavior control devices are known, which reduce a drive force of a vehicle according to a yaw rate related amount (e.g., yaw acceleration) corresponding to a steering operation by a driver, so as to promptly produce a deceleration in the vehicle when the driver starts the steering operation, and promptly apply a sufficient load on front wheels (drive wheels). For example, JP2014-166014A discloses such a device. According to such a vehicle behavior control device, by applying the load on the front wheels when the steering operation is started, a friction force between the front wheels and a road surface increases and a cornering force of the front wheels increases, and therefore, turning performance of the vehicle in a start of entering a curve improves, and responsiveness to a turning operation of the steering improves. Thus, a vehicle behavior intended by the driver is achieved.
Meanwhile, in a vehicle with an internal combustion engine, such as a gasoline engine or a diesel engine, a control device for controlling the engine determines a target torque based on an operating state of the vehicle (e.g., various operations of an accelerator pedal, a brake pedal, a steering, etc. performed by a driver, a traveling environment, such as a vehicle speed, an atmospheric temperature, an atmospheric pressure, a road gradient, a road surface μ, etc.), and controls the engine to output the target torque.
When the target torque is sharply changed, if the engine is controlled to reflect the change of the target torque as it is in an output torque, a sharp acceleration/deceleration is produced in the vehicle and a person on board may feel uncomfortable. Therefore, with the conventional control devices for engines, a chronological change of the target torque is smoothed to reduce the sharp acceleration/deceleration in the vehicle.
On the other hand, with the vehicle behavior control device described in JP2014-166014A, to accurately realize the vehicle behavior intended by the driver, the drive force of the vehicle needs to be reduced promptly in response to the steering operation. However, if the conventional control device for the engine smooths the chronological change of the target torque corresponding to this reduction request of the drive force, a response delay occurs in the drive force control of the vehicle in response to the steering operation by the driver. Therefore, a sufficient increase in the cornering force of the front wheels by the prompt application of the load on the front wheels cannot be achieved, and sufficient responsiveness to the turning operation of the steering cannot be secured. As a result, the vehicle behavior intended by the driver cannot accurately be achieved.